Immune Checkpoint Inhibitors in Gastrointestinal Cancers: Current Evidence and Future Directions

Cancer immunotherapy has long been established as an important treatment option for cancers. In particular, Immune Checkpoint Inhibitor (ICI) has been reported to be effective against various gastrointestinal cancers (esophageal cancer, gastric cancer, colorectal cancer); however, the treatment phase in which ICI should be used and how it should be incorporated into the treatment strategy vary depending on the cancer type being treated. Multiple clinical trials and basic research on ICIs are currently underway, and new insights from these results will continue to change the clinical treatment strategy of gastrointestinal cancers. While it is desirable to have an increasing number of treatment strategy options for gastrointestinal cancers, it is necessary to organize increasingly complex treatments and select more appropriate ICI-based treatments. In addition, as gastrointestinal cancers are being controlled through multidisciplinary treatment using ICI-based treatment, local control by conversion surgery is becoming an important treatment option. We may soon see an era in which gastrointestinal cancers can be systematically controlled with ICI-based treatment, while difficult-to-control lesions can be removed by conversion surgery. In this review, we summarize the evidence of ICI-based treatment for gastrointestinal cancers and provide an overview of the treatment strategies currently underway.